stihl bg55 or echo pb-251

I want to buy one or the other. I've read so much about the bg85 being so much more powerful than the bg55 that I went to the local dealer to ask why. He told me the 85 has a beefier engine with ball bearing mains and a different impeller/venturi/housing design. He said the flat versus round tube didn't matter on air speed. So I e-mailed stihl and they told me differently. They said the only difference between the two was the mufflers. One must be a cat. The housings are the same. The muffler gives more HP/air speed. The stihl has 2 rings, the echo has 1. The stihl ign. module is 2 years, the echo is lifetime. I like the cruise control on the echo. The echo is new. The stihl is tried and true. Any thoughts? Thanks for any feedback.